1. Field of the Invention
The present invention relates to a semiconductor laser device, and more particularly to a two-wavelength semiconductor laser device, which can emit light having two different wavelengths, and a method of manufacturing the same.
2. Description of the Related Art
Generally, a semiconductor laser device is a semiconductor device for emitting light amplified by stimulated emission, wherein the emitted light has a narrow frequency width (short wavelength characteristic) and ensures a high power, as well as excellent directivity. Due to the characteristics as mentioned above, the semiconductor laser device is widely applied to the field of optical fiber communication, multiplex communication, space communication and the like, as well as a light source for an optical pick-up apparatus of an optical disc system, such as CD, DVD and the like.
Recently, in the field of optical discs using the laser as the light source for recording and reproducing information, there is a need to provide a two-wavelength semiconductor laser device, which can oscillate at two different wavelengths. In particular, the two-wavelength semiconductor laser device is actively adopted as a light source for concurrently implementing a CD reproducer having a relatively low density and a DVD reproducer having a relatively high density. The two-wavelength semiconductor laser device has a laser diode for generating a beam having a wavelength of 780 nm on a single substrate and a structure for generating a beam having a wavelength of 650 nm.
FIG. 1 is a sectional side elevation illustrating a conventional two-wavelength semiconductor laser device.
Referring to FIG. 1, the conventional two-wavelength semiconductor laser device 10 includes a first semiconductor laser diode 10a and a second semiconductor laser diode 10b formed on a single substrate 11. The first and second semiconductor laser diodes 10a and 10b are separated by a predetermined isolation region, and are structured such that they emit light having fist and second wavelengths, respectively. The light having the first wavelength is laser light having a wavelength of 650 nm, and the light having the second wavelength is laser light having a wavelength of 780 nm.
Each of the first and second semiconductor laser diodes 10a and 10b may have an SBR (Selectively Buried Ridge) structure with a first conductive clad layer 12a or 12b, an active layer 13a or 13b, and a second conductive clad layer 14a or 14b sequentially laminated thereon. The SBR structure of the first and second semiconductor laser diodes 10a and 10b includes a second conductive clad layer 14a or 14b having a ridge structure, a first conductive material current shield layer 15a or 15b formed around the second conductive clad layer 14a or 14b, and a second conductive contact layer 16a or 16b connected with the second conductive clad layer 14a or 14b on the first conductive material current shield layer 15a or 15b. The substrate 11 is provided with a first electrode 17 acting as a common electrode at the bottom of the substrate 11 and the second conductive contact layers 16a and 16b are provided with second electrodes 18a and 18b, respectively, so that the first and second semiconductor laser diodes 10a and 10b can be independently driven.
According to one conventional method of manufacturing the two-wavelength semiconductor laser device, after being separately manufactured, the semiconductor laser diodes 10a and 10b are coupled onto the same substrate 11 by a die-bonding process. However, this method has problems in that in addition to the manufacturing process of the semiconductor laser diodes 10a and 10b, a separate bonding process is required, thereby complicating the overall process. Moreover, this method has problems in that bad alignment can be caused in the die-bonding process, and in that miniaturization of a semiconductor chip is difficult.
According to another conventional method, after a mask (not shown) is formed such that only a first region is exposed on a single substrate 11, a first semiconductor laser diode 10a for emitting light having a first wavelength is formed on the first region, and after removing the mask, a second semiconductor laser diode 10b for emitting light having a second wavelength is formed at a second region on the substrate 11.
However, the other method requires repetitious formation and removal processes for the mask. Further, since crystal growth processes for growing the first and second semiconductor laser diodes must be suspended, there still exists the problem of complicating the total process. Particularly, as the surface corresponding to the second region of the substrate 11 is damaged due to an etching process for removing the mask, the method has a disadvantage causing a problem in the crystal growth process for the second semiconductor laser diode 10b. 